Release Of Organic Carbon Research Articles

Efficient degradation of 2,4-dichlorophenoxyacetic acid by peroxymonosulfate/magnetic copper ferrite nanoparticles/ozone: A novel combination of advanced oxidation processes

In this study, magnetic copper ferrite nano-particles (CuFe2O4, MCFNs) were used in ozone/peroxymonosulfate (PMS) system to degrade 2,4-dichlorophenoxyacetic acid (2,4-D). The characteristics of MCFNs, operational parameters of PMS/MCFNs/ozone system and the kinetic of 2,4-D degradation were evaluated. Complete degradation of 20.0mg/L 2,4-D was obtained in pH=6.0, PMS=2.0mM, ozone=16.0mg/L, MCFNs=0.20g/L and 40min reaction time. Reusability and stability experiments indicated that MCFNs were effective in several runs. Furthermore, simultaneous presence of ozone and PMS, increased iron and copper leaching in solution. Several binary and ternary systems were evaluated on 2,4-D removal by combination of oxidants (PMS and ozone), catalyst (CuFe2O4) and its components (CuO and Fe2O3). MCFNs provided higher degradation compared to CuO and Fe2O3 in ozone/PMS system. Among the anions, bicarbonate, phosphate and nitrite showed a negative effect on the performance of ozone/MCFNs/PMS system. Moreover, a decrease in 2,4-D degradation was observed in real different matrices. The results of scavenging experiments showed that several oxidative agents were effective in degrading of 2,4-D including SO4−, HO, O2− and 1O2. The presence of ozone increased oxidative role of HO, O2− and 1O2 in the main system. Mineralization of 2,4-D was assessed by Total Organic Carbon (TOC) and chloride release. 67.3% of TOC and 42.7% of chlorine of 2,4-D were removed. A significant increase in biodegradability and a considerable decrease in toxicity of 2,4-D were obtained after treatment by PMS/MCFNs/ozone system. Finally, the by-products formed during PMS/MCFNs/ozone process were identified through LC–MS analysis.

Macrophyte beds in a subtropical reservoir shifted from a nutrient sink to a source after drying then rewetting

AbstractMacrophytes play a key role in assimilating and storing nutrients in shallow aquatic ecosystems, but their capacity to act as a long‐term nutrient sink can be affected by water level fluctuations. Water level drawdown in reservoirs followed by rewetting may mobilise a significant nutrient pool. These nutrients can be stored in the littoral zone in dead or dormant macrophytes, and in the desiccated sediments within the macrophyte beds. However, the contribution of desiccated macrophyte beds to nutrient release upon rewetting has not been well quantified.Our study examined the effect of rewetting the previously desiccated waterlilyNymphoides indica(Menyanthaceae) in treatments (1) without sediments (N.i.−Sed), and (2) with sediments inN. indicabeds (N.i.+Sed) on water quality.We found that longer drying duration increased dissolved nutrients (nitrate/nitrite, ammonium and total dissolved organic nitrogen/phosphorus) and organic carbon release fromN.i.+Sed andN.i.−Sed treatments after rewetting. In theN.i.+Sed treatment with <4 weeks of desiccation, allN. indicaplants regenerated from roots after subsequent rewetting. In addition, the resulting nutrient/carbon release was not significantly different to the control treatment which did not have desiccation. A significant increase in dissolved nutrient and carbon concentrations in the water column was found in treatments with more than 10 weeks of desiccation followed by rewetting. This coincided with the sediment reaching its minimum moisture content. Furthermore, chlorophylla(Chl‐a) concentrations in the overlying water also increased with more than 10 weeks of desiccation, presumably in response to the increased nutrient availability and the removal of competition for nutrients from macrophytes.On the basis of our laboratory experiments, we calculated the potential effect of desiccated and rewettedN. indicabeds on water quality in a localN. indica‐dominated reservoir after water level drawdown. We also separated the contribution ofN. indicaplants from their macrophyte beds on water quality changes. Fourteen days after rewetting, the total dissolved nutrients released fromN. indicaalone (N.i.−Sed) could contribute 0.5% of the total nitrogen and 29% of total phosphorus to the water column concentrations in the whole reservoir. In contrast,N. indicabeds (N.i.+Sed) contributed more total dissolved nitrogen (4.3%) but less total dissolved phosphorus (0.3%) release into the water column. The higher nitrogen release for theN.i.+Sed treatment was likely due to the organic matter decomposition in the sediment in macrophyte beds. In contrast, the less dissolved phosphorus release, compared with theN. indicaalone, was likely the result of phosphate adsorption by previously desiccated soil particles and/or assimilation by phytoplankton, since the phytoplankton biomass (as measured by Chl‐aconcentrations) was significantly higher in theN.i.+Sed treatment.This study highlights the importance of managing both the duration and rate of water level drawdown in reservoirs to prevent rooted macrophytes, likeN. indica,from becoming a source of nutrients, which may cause deterioration in water quality.

Deforestation in Amazonia impacts riverine carbon dynamics

Abstract. Fluxes of organic and inorganic carbon within the Amazon basin are considerably controlled by annual flooding, which triggers the export of terrigenous organic material to the river and ultimately to the Atlantic Ocean. The amount of carbon imported to the river and the further conversion, transport and export of it depend on temperature, atmospheric CO2, terrestrial productivity and carbon storage, as well as discharge. Both terrestrial productivity and discharge are influenced by climate and land use change. The coupled LPJmL and RivCM model system (Langerwisch et al., 2016) has been applied to assess the combined impacts of climate and land use change on the Amazon riverine carbon dynamics. Vegetation dynamics (in LPJmL) as well as export and conversion of terrigenous carbon to and within the river (RivCM) are included. The model system has been applied for the years 1901 to 2099 under two deforestation scenarios and with climate forcing of three SRES emission scenarios, each for five climate models. We find that high deforestation (business-as-usual scenario) will strongly decrease (locally by up to 90 %) riverine particulate and dissolved organic carbon amount until the end of the current century. At the same time, increase in discharge leaves net carbon transport during the first decades of the century roughly unchanged only if a sufficient area is still forested. After 2050 the amount of transported carbon will decrease drastically. In contrast to that, increased temperature and atmospheric CO2 concentration determine the amount of riverine inorganic carbon stored in the Amazon basin. Higher atmospheric CO2 concentrations increase riverine inorganic carbon amount by up to 20 % (SRES A2). The changes in riverine carbon fluxes have direct effects on carbon export, either to the atmosphere via outgassing or to the Atlantic Ocean via discharge. The outgassed carbon will increase slightly in the Amazon basin, but can be regionally reduced by up to 60 % due to deforestation. The discharge of organic carbon to the ocean will be reduced by about 40 % under the most severe deforestation and climate change scenario. These changes would have local and regional consequences on the carbon balance and habitat characteristics in the Amazon basin itself as well as in the adjacent Atlantic Ocean.

Increased temperature, rather than elevated CO2, modulates the carbon assimilation of the Arctic kelps Saccharina latissima and Laminaria solidungula

Ocean acidification and warming are affecting with special intensity the Arctic Ocean. Arctic coastal ecosystems are dominated by kelp forests with a high biomass production, which are expected to be directly affected by the increases in CO2 and temperature. This study presents the different physiological responses of the Arctic kelps Saccharina latissima and Laminaria solidungula from Kongsfjorden (Svalbard) cultured at 4 and 9 °C in combination with current (390 ppm) and increased (1200 ppm) levels of atmospheric CO2. Both species were largely unaffected by increased CO2 conditions. Carbon fixation was not influenced by CO2, indicating that photosynthesis was C-saturated at present levels, and 13C isotopic discrimination values from algal tissue suggested no deactivation of carbon concentrating mechanisms at increased CO2 levels. Inhibition of photosynthesis by carbonic anhydrases (CAs) inhibitors highlighted the important role of external CAs in inorganic carbon acquisition in Arctic kelps. Saccharina latissima showed a significantly higher growth rate at 9 °C than at 4 °C, probably due to the decrease in the dark respiration rate observed. Growth rate of L. solidungula was not affected by temperature or CO2, and increases in photosynthesis at 9 °C could be partially related to a higher dissolved organic carbon release rate. The photochemical performance of both species was not altered by any of the treatments. These results suggest that S. latissima might be more benefited than L. solidungula in a future warmer Arctic, while both populations seem to be resilient to higher CO2 concentrations.

Pre-treating biosorbents for purification of bioethanol from aqueous solution

ABSTRACTCost-effective biosorbents made from the byproducts of agriculture, forest, and related industries, such as barley straw, canola meal, and wood sawdust, have significant water adsorption capacity, showing a great potential for selective water removal from bioalcohols to produce fuel grade products. However, there is a challenge that the biosorbents are not stable when they come in contact with aqueous solution. There are organic carbons released from biosorbents to liquid phase, which needs to be addressed before this technology is applied in the industrial purification of bioalcohols. In this work, raw barley straw representing an abundant group of cellulosic materials in the above-mentioned industries was used as a model material. A methodology of chemical and physical treatment was developed to treat barley straw which successfully enhanced the stability and reduced the total organic carbon release from the material into the aqueous solution. In addition, the pre-treated barley straw biosorbent had significantly increased micropores, and the Brunauer--Emmett--Teller surface area favored by water adsorption compared with raw barley straw. It also had higher water uptake and dynamic water adsorption selectivity. The pre-treated barley straw was able to selectively remove water and generate concentrated ethanol.

Unexpected release of phosphate and organic carbon to streams linked to declining nitrogen depositions.

Reductions in emissions have successfully led to a regional decline in atmospheric nitrogen depositions over the past 20years. By analyzing long-term data from 110 mountainous streams draining into German drinking water reservoirs, nitrate concentrations indeed declined in the majority of catchments. Furthermore, our meta-analysis indicates that the declining nitrate levels are linked to the release of dissolved iron to streams likely due to a reductive dissolution of iron(III) minerals in riparian wetland soils. This dissolution process mobilized adsorbed compounds, such as phosphate, dissolved organic carbon and arsenic, resulting in concentration increases in the streams and higher inputs to receiving drinking water reservoirs. Reductive mobilization was most significant in catchments with stream nitrate concentrations <6mgL-1 . Here, nitrate, as a competing electron acceptor, was too low in concentration to inhibit microbial iron(III) reduction. Consequently, observed trends were strongest in forested catchments, where nitrate concentrations were unaffected by agricultural and urban sources and which were therefore sensitive to reductions of atmospheric nitrogen depositions. We conclude that there is strong evidence that the decline in nitrogen deposition toward pre-industrial conditions lowers the redox buffer in riparian soils, destabilizing formerly fixed problematic compounds, and results in serious implications for water quality.

Short-term leaching dynamics of three peatland plant species reveals how shifts in plant communities may affect decomposition processes

Foliar litter is the main input of organic carbon to many soils, and thus litter decomposition processes are integral to our understanding of carbon dynamics in soil systems. Despite the short duration of the leaching phase of decomposition, a considerable amount of mass loss can occur providing a valuable energy source for microbes, and influencing leaf litter chemistry for subsequent microbial decomposition. At the same time, differences in plant species and their functional traits play a role in decomposition dynamics, particularly in consideration of shifting plant communities or changes in leaf chemistry under climate change. Here we investigate the short-term leaching decomposition dynamics of three boreal peatland plant species (Carex magellanica, Chamaedaphne calyculata, Sphagnum magellanicum) grown under ambient and elevated levels of atmospheric CO2. Litter chemistry was significantly different among all three plant species. In addition, plant tissues grown under elevated CO2 showed lower total C and total N than plants grown under ambient CO2. After leaching, however litter from plants grown under elevated CO2 conditions were not significantly different in total C values compared to plants grown under ambient CO2 conditions. Mass loss corresponded with the total dissolved organic carbon release across all species and was greatest in Chamaedaphne, a woody shrub; measures of carbon lability (SUVA254) were significantly greater in vascular plant species compared to Sphagnum moss. Mass loss was reduced in plants grown under elevated CO2 conditions, suggesting allocation to more non-soluble structural compounds. Placing our results within a climate change scenario where peatland plant community compositional shifts from mosses to graminoids and woody shrubs have been observed, we suggest that greater amounts of more labile carbon released from vascular plant species indicates a shift to more decomposable litters with the potential to stimulate microbial growth and activity.

Water quality following extensive beetle-induced tree mortality: Interplay of aromatic carbon loading, disinfection byproducts, and hydrologic drivers

The recent bark beetle epidemic across western North America may impact water quality as a result of elevated organic carbon release and hydrologic shifts associated with extensive tree dieback. Analysis of quarterly municipal monitoring data from 2004 to 2014 with discretization of six water treatment facilities in the Rocky Mountains by extent of beetle impact revealed a significant increasing trend in total organic carbon (TOC) and total trihalomethane (TTHM) production within high (≳50% areal infestation) beetle-impacted watersheds while no or insignificant trends were found in watersheds with lower impact levels. Alarmingly, the TTHM concentration trend in the high impact sites exceeded regulatory maximum contaminant levels during the most recent two years of analysis (2013–14). To evaluate seasonal differences, explore the interplay of water quality and hydrologic processes, and eliminate variability associated with municipal reporting, these treatment facilities were targeted for more detailed surface water sampling and characterization. Surface water samples collected from high impact watersheds exhibited significantly higher TOC, aromatic signatures, and disinfection byproduct (DBP) formation potential than watersheds with lower infestation levels. Spectroscopic analyses of surface water samples indicated that these heightened DBP precursor levels are a function of both elevated TOC loading and increased aromatic character. This association was heightened during precipitation and runoff events in high impact sites, supporting the hypothesis that altered hydrologic flow paths resulting from tree mortality mobilize organic carbon and elevate DBP formation potential for several months after runoff ceases. The historical trends found here likely underestimate the full extent of TTHM shifts due to monitoring biases with the extended seasonal release of DBP precursors increasing the potential for human exposure. Collectively, our analysis suggests that while water quality impacts continue to rise nearly one decade after infestation, significant increases in TOC mobilization and DBP precursors are limited to watersheds that experience extensive tree mortality.

Effect of recurrent sediment resuspension-deposition events on bioavailability of polycyclic aromatic hydrocarbons in aquatic environments

To investigate the effect of recurrent sediment resuspension-deposition events (RSRDEs) on bioavailability of polycyclic aromatic hydrocarbons (PAHs) in aquatic environments, a modified device was used to simulate three resuspension-deposition events with the sediment collected from the Yellow River. The results showed that the dissolved organic carbon (DOC)-water distribution coefficients of PAHs decreased with time during the first resuspension-deposition period. It indicates that some PAHs associated with organic carbon (OC) in suspended sediment (SPS) desorbed with the release of OC and became DOC-associated PAHs in the overlying water, then the PAHs desorbed from the DOC and became freely dissolved. After first 2-h suspension, only 1.90% of phenanthrene, 2.98% of pyrene, and 0.33% of chrysene in the overlying water came from pore-water; at least 61.6%, 89.6%, and 95.3% came from DOC-associated PAHs in SPS and the rests were released from the insoluble OC in SPS. The maximum desorption ratios in the original sediment were 20%, 12%, and 14% for phenanthrene, pyrene, and chrysene, respectively during the first resuspension-deposition event. The SPS concentration followed the sequence of the third>second>first resuspension event. This was because RSRDEs changed the SPS particle size and enhanced floc formation. There was no significant difference in the total dissolved PAH concentrations among the three resuspension events, while their freely dissolved concentrations followed the sequence of the third>second>first resuspension event. During deposition periods, more than half of the total/freely dissolved PAHs released during suspension still existed in the overlying water after 70-h deposition. This study suggests that the RSRDEs will increase the bioavailability of PAHs in aquatic environments, especially near the sediment-water interface, and the potential effects of PAHs during RSRDEs on fish/human in rivers and lakes should be considered in future management.

Effects of visible light radiation on macrophyte litter degradation and nutrient release in water samples from a eutrophic shallow lake

ABSTRACTVisible light is a major fraction of the solar spectrum; however, information on visible light radiation of macrophyte detritus is lacking. In this study, we conducted a microcosm experiment to assess the effects of visible light radiation on degradation of two litter species: Potamogeton malaianus (P. malaianus) and Phragmites australis (Ph. australis). This research represents an investigation of mass loss, microbial activity and nutrients released over a period of 168 days. Overall, we found that visible light radiation had significant effects on litter decomposition, but it did not affect the microbial activities which degrade cellulose and lignin. The decomposition rate order of the three components in P. malaianus and Ph. australis in treatments was: cellulose > hemicellulose > lignin. The visible light radiation mainly affected the degradation of lignin, which is the primary compound in litter susceptible to photodegradation. The exposure to visible light radiation up to 17.6 Wm−2 stimulated the dissolved organic carbon release and reduced the molecular weight to less reactive. Meanwhile, no obvious difference in nutrient contents (TP, TN, NO3–N, NO2–N, and NH3–N) was observed among different visible light intensities. The results of this study contribute to better understanding of the photochemical behaviour of macrophyte litter in shallow lakes.

Transport and fate of estrogens from swine manure in a biochar amended sandy soil in a freeze-thaw environment

Under growing concerns of their possible adverse effects on ecosystems, natural steroidal sex hormones, originating from liquid swine manure, have been detected at trace concentrations in a number of natural environments. Various studies have highlighted biochar’s potential in adsorbing such hormones, given its structural and physiochemical properties. The remaining hormone adsorption capacity of a 1% slow pyrolysis biochar topsoil amendment was tested after one year of its application to a sandy soil, housed in outdoor lysimeters irrigated with simulated rainfall. The fate and transport of estrogens, over a 46-day period following the incorporation of liquid swine manure (4 g N/L @ 16 L/m2) into the topsoil, was monitored in biochar-amended and non-amended lysimeters. While in the first year of biochar application, a significant spatial-temporal stratification of steroidal sex hormones had been observed in the biochar-amended soil (vs. non-amended soil), in the second year biochar absorbed hormones to a considerably lesser degree. Concurring with the findings of laboratory batch adsorption experiments on fresh and used biochar, the present study showed that 1% slow pyrolysis biochar`s capacity to absorb sex hormones (estrogens) released from liquid swine manure in sandy soil decreases during second year. This is presumably the freezing and thawing weather conditions of experimental site that resulted in biochar surface degradation leading to the release of soluble organic carbon, thereby facilitating a heightened mobility of hormones and their resultant leaching to lower depths in the soil profile.

PEX and PP Water Pipes: Assimilable Carbon, Chemicals, and Odors

Eleven brands of plastic drinking water pipe were evaluated for assimilable organic carbon (AOC) release at 23°C for 28 days: polyvinyl chloride, high‐density polyethylene, polypropylene (PP), and cross‐linked polyethylene (PEX) pipes. Three of eight PEX pipe brands exceeded a 100 µg/L AOC microbial regrowth threshold for the first exposure period, and no brands exceeded this value on day 28. No AOC increase was found for PP or PEX‐a1 pipes; the remaining pipe brands contributed marginal AOC levels. Pipe water quality impacts were more fully evaluated for two PEX‐b brands and one PP brand. PEX pipes caused greater odor than the PP pipe and released more organic carbon as well as volatile and semi‐volatile organic compounds. Water quality impacts were less after 30 days. Regulated and unregulated contaminants were found in three PEX plumbing systems. Drinking water odors were attributed to toluene, ethyl‐tert‐butyl ether, and unidentified contaminants.

Asynchronous reductive release of iron and organic carbon from hematite–humic acid complexes

Solid-phase iron (Fe) plays an important role in the accumulation and stabilization of soil organic matter (SOM). However, ferric minerals are subject to redox reactions, which can compromise the stability of Fe-bound SOM. To date, there is limited information available concerning the fate of Fe-bound SOM during redox reactions at Fe mineral surfaces. In this study, we investigated the release kinetics of hematite-bound organic carbon (OC) during the abiotic reduction of hematite–humic acid (HA) complexes by dithionite, to elucidate important processes governing the stability and fate of organic matter during the redox processes. Our results indicate that the reductive release of Fe obeyed first-order kinetics with release rate constants of 6.67–13.0×10−3min−1. The Fe-bound OC was released rapidly during the initial stage with release rate constants of 0.011–1.49min−1, and then became stable with residual fractions of 4.6–58.2% between 120 and 240min. The release rate of aromatic OC was much faster than for the non-aromatic fraction of HA, and 90% of aromatic OC was released within the first hour for most samples. Our findings show that in the reductive reaction the mobilization of Fe-bound OC was asynchronous with the reduction of Fe, and aromatic OC was released more readily than other components of SOM. This study highlights the importance of evaluating the release of SOM bound with Fe during the redox reactions, especially the influence of the physicochemical properties of SOM.

Cellulase activity and dissolved organic carbon release from lignocellulose macrophyte-derived in four trophic conditions.

Considering the importance of lignocellulose macrophyte-derived for the energy flux in aquatic ecosystems and the nutrient concentrations as a function of force which influences the decomposition process, this study aims to relate the enzymatic activity and lignocellulose hydrolysis in different trophic statuses. Water samples and two macrophyte species were collected from the littoral zone of a subtropical Brazilian Reservoir. A lignocellulosic matrix was obtained using aqueous extraction of dried plant material (≈40 °C). Incubations for decomposition of the lignocellulosic matrix were prepared using lignocelluloses, inoculums and filtered water simulating different trophic statuses with the same N:P ratio. The particulate organic carbon and dissolved organic carbon (POC and DOC, respectively) were quantified, the cellulase enzymatic activity was measured by releasing reducing sugars and immobilized carbon was analyzed by filtration. During the cellulose degradation indicated by the cellulase activity, the dissolved organic carbon daily rate and enzyme activity increased. It was related to a fast hydrolysable fraction of cellulose that contributed to short-term carbon immobilization (ca. 10 days). After approximately 20 days, the dissolved organic carbon and enzyme activity were inversely correlated suggesting that the respiration of microorganisms was responsible for carbon mineralization. Cellulose was an important resource in low nutrient conditions (oligotrophic). However, the detritus quality played a major role in the lignocelluloses degradation (i.e., enzyme activity) and carbon release.

Biomass offsets little or none of permafrost carbon release from soils, streams, and wildfire: an expert assessment

As the permafrost region warms, its large organic carbon pool will be increasingly vulnerable to decomposition, combustion, and hydrologic export. Models predict that some portion of this release will be offset by increased production of Arctic and boreal biomass; however, the lack of robust estimates of net carbon balance increases the risk of further overshooting international emissions targets. Precise empirical or model-based assessments of the critical factors driving carbon balance are unlikely in the near future, so to address this gap, we present estimates from 98 permafrost-region experts of the response of biomass, wildfire, and hydrologic carbon flux to climate change. Results suggest that contrary to model projections, total permafrost-region biomass could decrease due to water stress and disturbance, factors that are not adequately incorporated in current models. Assessments indicate that end-of-the-century organic carbon release from Arctic rivers and collapsing coastlines could increase by 75% while carbon loss via burning could increase four-fold. Experts identified water balance, shifts in vegetation community, and permafrost degradation as the key sources of uncertainty in predicting future system response. In combination with previous findings, results suggest the permafrost region will become a carbon source to the atmosphere by 2100 regardless of warming scenario but that 65%–85% of permafrost carbon release can still be avoided if human emissions are actively reduced.

Effect of light and nutrient availability on the release of dissolved organic carbon (DOC) by Caribbean turf algae.

Turf algae increasingly dominate benthic communities on coral reefs. Given their abundance and high dissolved organic carbon (DOC) release rates, turf algae are considered important contributors to the DOC pool on modern reefs. The release of photosynthetically fixed carbon as DOC generally, but not always, increases with increased light availability. Nutrient availability was proposed as an additional factor to explain these conflicting observations. To address this proposed but untested hypothesis, we documented the interactive contributions of light and nutrient availability on the release of DOC by turf algae. DOC release rates and oxygen production were quantified in incubation experiments at two light levels (full and reduced light) and two nutrient treatments (natural seawater and enriched seawater). In natural seawater, DOC release at full light was four times higher than at reduced light. When nutrients were added, DOC release rates at both light levels were similar to the natural seawater treatment at full light. Our results therefore show that low light in combination with low nutrient availability reduces the release of DOC by turf algae and that light and nutrient availability interactively determine DOC release rates by this important component of Caribbean reef communities.

Heterogeneity in leaf litter decomposition in a temporary Mediterranean stream during flow fragmentation

In temporary Mediterranean streams, flow fragmentation during summer droughts originates an ephemeral mosaic of terrestrial and aquatic habitat types. The heterogeneity of habitat types implies a particular ecosystem functioning in temporary streams that is still poorly understood. We assessed the initial phases of leaf litter decomposition in selected habitat types: running waters, isolated pools and moist and dry streambed sediments. We used coarse-mesh litter bags containing Populus nigra leaves to examine decomposition rates, microbial biomass, macroinvertebrate abundance and dissolved organic carbon (DOC) release rates in each habitat type over an 11-day period in late summer. We detected faster decomposition rates in aquatic (running waters and isolated pools) than in terrestrial habitats (moist and dry streambed sediments). Under aquatic conditions, decomposition was characterized by intense leaching and early microbial colonization, which swiftly started to decompose litter. Microbial colonization in isolated pools was primarily dominated by bacteria, whereas in running waters fungal biomass predominated. Under terrestrial conditions, leaves were most often affected by abiotic processes that resulted in small mass losses. We found a substantial decrease in DOC release rates in both aquatic habitats within the first days of the study, whereas DOC release rates remained relatively stable in the moist and dry sediments. This suggests that leaves play different roles as a DOC source during and after flow fragmentation. Overall, our results revealed that leaf decomposition is heterogeneous during flow fragmentation, which has implications related to DOC utilization that should be considered in future regional carbon budgets.

Effect of vegetated filter strips on transport and deposition rates of Escherichia coli in overland flow in the eastern escarpments of the Mau Forest, Njoro River Watershed, Kenya.

The fate and transport of Escherichia coli (E. coli) in lotic waters through vegetated filter strips (VFSs) was evaluated in a field model pasture, utilizing VFSMOD Windows along with direct pathogen testing. This study assessed effects of VFS on transport and deposition rates of E. coli in lotic overland flow waters. The VFS measured 44 m long by 40 m wide, covering an area of 1584 m2 and land slope of 15 %. Cowpat was applied onto the model pasture and washed by overland flow into the VFS. The 4-methylumbelliferyl β-D-glucuronide substrate confirmed the identity of E. coli prior to cowpat application and after isolating them from soil using centrifugation and membrane filtration techniques. Napier grass root system recorded the highest recovery rates of E. coli at 99.9 % along the length of VFS III. This efficiency reduced significantly (p < 0.05; df = 29) to 95 % in Kikuyu grass and 75 % in Couch grass-Buffer grass. The data demonstrated similarity in transport of manure-borne E. coli and organic carbon (OC) through all the simulated VFS. These results indicated that OC could be used as a true natural tracer of manure-borne E. coli, a pollution indicator organism of lentic and lotic surface waters provided the OC release kinetics from cowpat were similar to that of E. coli kinetics. Thus, efficient filtering to reduce E. coli concentrations and load in overland flows requires managing combined grass species, agro-pastoral systems models and dispersed or preferential flows to enhance surface water quality standards.

Decadal carbon discharge by a mountain stream is dominated by coarse organic matter

Rapid erosion in mountain forests results in high rates of biospheric particulate organic carbon (POC) export by rivers, which can contribute to atmospheric carbon dioxide drawdown. However, coarse POC (CPOC) carried by particles >∼1 mm is rarely quantified. In a forested pre-Alpine catchment, we measured CPOC transport rates and found that they increase more rapidly with water discharge than fine POC (<1 mm) and dissolved organic carbon (DOC). As a result, decadal estimates of CPOC yield of 12.3 ± 1.9 t C km–2 yr–1 are higher than for fine POC and DOC, even when excluding 4 extreme flood events. When including these floods, CPOC dominates organic carbon discharge (∼80%). Most CPOC (69%) was water logged and denser than water, suggesting that CPOC has the potential to contribute to long-term sedimentary burial. Global fluxes remain poorly constrained, but if the transport behavior of CPOC shown here is common to other mountain streams and rivers, then neglecting CPOC discharge could lead to a large underestimation of the global transfer of biospheric POC from land to ocean.

Dynamics of dissolved organic carbon release from a permafrost wetland catchment in northeast China

Summary A large reservoir of organic carbon is stored in the permafrost region. Therefore, understanding the export of dissolved organic carbon (DOC) from rivers in the permafrost zone is important in the context of climate change. This study investigated the dynamics of DOC export from the wetlands of the Kandu River catchment located in a cold temperate region in northeast China during the growing seasons of 2011 and 2012. Our findings indicated that subsurface flow was the primary runoff pathway that transports DOC from wetland soil to stream discharge. The organic–mineral soil structure resulted in substantial differences in water sources, as well as in DOC resources, between the flood and base flow volume during the growing seasons. The active layer depth is key, as it affects runoff generation and the DOC concentration and chemical characteristics of stream discharge. The DOC flux from our study area was estimated to be up to 1039.66 t during the growing season, which represents more than one third of the net ecosystem exchange (NEE) in wetlands. Given the expected increase in air temperature and precipitation, our results indicate that there will be an increase in the total DOC flux for the study region in the future as a result of increased DOC concentration.